Process for production of polycarbonamides



Jan. 24, 1967 E. P. BRIGNAC 3,300,449

PROCESS FOR PRODUCTION OF POLYCARBONAMIDES Original Filed Oct. 4, 1962SPRAY CONDENSER 19 FILTER CRUDE DIAMINE FINISHER STORAGE POLYMER -|5INVENTOR.

EDMOND P. BRIGNAC ATTORNEY United States Patent 3,300,449 PROCESS FORPRODUCTION OF POLYCARBONAMIDES Edmond P. Brignac, Pensacola, Fla.,assignor to Monsanto Company, St. Louis, Mo., a corporation of DelawareContinuation of application Ser. No. 228,496, Oct. 4, 1962. Thisapplication Oct. 19, 1964, Ser. No. 406,216 1 Claim. (Cl. 260-78) Thisis a continuation of application Serial No. 228,496, filed October 4,1962, now abandoned.

This invention relates to an apparatus and an improved process for theproduct-ion of high molecular weight polymers, especially those preparedby condensation-type reactions, such as polyamides, polyesters, and thelike. More particularly, this invention relates to an apparatus and animproved process for the continuous production of linearpolycarbonamides of a type characterized by high molecular weightincluding those particularly useful in the formation of shaped articlessuch as fibers, filaments, and the like.

The production of the linear condensation polymers from polymer formingreactants has assumed increasing commercial importance throughoutvarious industries. It is because of the increasing commercialimportance that new apparatus and improved processes which give improvedqu-ality productsin a more economical :manner are necessary.

In the formation of such linear polymers, particularly those of the typehaving properties which include film and fiber forming properties, thepolymeric end product may be a polycarbonamide which is formed fromliquid compositions comprising polycarbonamide forming reactants. In oneexample of the formation of polycarbonamides, such as nylons and thelike, a solution of polycarbonatmide forming composition which usuallycontains water or other solvent is subjected to superatmosphericpressures and polycarbonamide forming temperatures to carry out thepolycondensation or polycarbonamide forming reaction. As thepolycondensation of the polycarbonamide form-ing composition progresses,the viscosity of the polycarbonamide reaction mass increases in awellknown manner until the desired degree of polymerization is obtained.

Previous polycarbonamide forming compositions comprise water solutionsof hexamethylenediamine and adipic acid, and the preparation of thesesolutions commercially entails great amounts of time and handling. Inorder to insure filaments or fibers of high quality and excellentproperties, it has been thought in the past that considerable blendingof the manufactured hexamethylenediamine, as well as blending of themanufactured adipic acid, was necessary to obtain bothhexamethylenediamine and adipic acid of uniform quality and high purity.

Further, after blending of the hexamethylenediamine and adipic acid,these reactants are mixed and diluted with water to a 40 to 60 percentconcentration so that the reactant solution can be stored for periodswithout precipitation or other loss of the polycarbonamide formingreactants. To insure further the uniform quality of product, these watersolutions of the reactants or nylon salt solutions are blended withother similar nylon salt solutions.

Additional treating operations are also carried out for other purposes.The nylon salt solution is treated with activated carbon so that theresultant polymer will have good clarity or whiteness, and the pH of thesolution is adjusted prior to the beginning of the commercialpolymerization operation so that the resultant polymer will have uniformdye receptivity and a uniform variation'of polymer molecular weight.

3,300,449 Patented Jan. 24, 1967 Even though all the above mentionedpretreatment operations appear to be traditional in the manufacture ofhigh molecular weight polycarbonamides such as nylon, it has not beenshown that these treatments are necessary or even advisable for nylonpolymer which is to be used in certain specific applications wheretensile strength, elasticity, and other similar physical properties areof prime importance. An example of such an application in the use ofnylon as a reinforcing matrix in the manufacture of automobile and trucktires.

Further, in the first steps of the formation of polycarbonamides such asnylon, previous processes require the heating of the nylon salt solutionat superatmospheric pressures to remove the water solvent, and since thepolymerization of the reactants is one of condensation wherein water isreleased as the polymer is formed, the removal of the water of solutionas well as the water of formation from the polymer without thermaldegradation of the polymer during such removal is one of the criticalproblems of all previous commercial polycarbonamide forming processes.

Previously, all efforts to mix polycarbonamide reactants such as adipicacid and hexamethylenediamine in the ab sence of a suitable solvent havebeen unsuccessful because of the strong propensity of these reactants toform agglomerate masses which cannot be melted for reactant purposes dueto the low heat transfer coetficient and smooth surface of theagglomerate mass. These agglomerate masses which remain unmelted createa non-homogeneous reactant system which prevents polymerization andcauses excessive pressure drop and unnecessary shutdowns in commercialcontinuous polymerization apparatus.

It is, therefore, a first object of this invention to provide a new andnovel apparatus and an improved process for the manufacture ofpolycarbonamides in the absence of solvent for the polycarbonamidereactants.

Another object of this invention is to provide a new apparatus andprocess for the manufacture of polycarbonamides which is more economicalthan previously known processes.

Still another object of this invention is to provide an apparatus andprocess for manufacture of polycarbonamides which will reduce oreliminate thermal degradation of the polymer during its formation.

A further object of this invention is to provide a new and novelapparatus and process for the manufacture of polycarbonamides in ashorter period of time than was previously possible.

Other objects and advantages of this invention will become apparent fromthe following description thereof considered in connection with thedrawing.

The objects of this invention are accomplished by providingsimultaneously, under proper rheological and pressure conditions,controlled volumes of refined hexamethylenediamine and molten adipicacid to a high temperature, high surface area to volume ratio reactionzone; causing the reactants to be retained in the reaction zone for ashort period of time; removing the reactants from the reaction zone to asubsequent reduced pressure zone where vapor is permitted to separatefrom the polymer forming reactants; and then causing the reactants to befinished or polymerized to the desired degree of polymerization in astandard nylon screw finisher or other similar finishing apparatussuitable for the purpose. The vapors which are formed in the reducedpressure zone are subjected to appropriate means, such as spraycondensing and filtering to recover hexamethylenediamine vaporized inthis step, and the recovered hexamethylenediamine is recycled, afternecessary purification by refining or other means, to the beginning ofthe process.

The novel features which are believed to be characteristic of thisinvention are set forth with particularity in the appended claim,however, the invention itself, both as to its organization and itsmethod of operation, may be understood best by reference to thefollowing description taken in conjunction with the accompanying drawingin which:

FIGURE 1 is a flow sheet or diagram illustrating a polymerizationprocess carried out in accordance with the invention.

Although, in general, any suitable polymer forming composition may beprocessed with the novel apparatus and improved process of thisinvention, those materials capable of undergoing polycondensation andcapable of producing high molecular weight compounds, e.g., those havingfiber forming characteristics, are preferable. It is with referencethereto that the novel method of the invention will be described.

Polymer forming compositions suitable for preparing fiber formingpolymers may be of any type from which polycarbonamides are prepared andit is for the preparation of polycarbonamides, which includes thecommercially produced nylons, that the description of the invention willbe directed specifically hereinafter.

Referring now to FIGURE 1, there is shown schematically one embodimentof the novel process for making linear polymers contemplated by thisinvention. In this embodiment, high purity molten adipic acid fromadipic acid melter 1, is fed by line 2, to pump 3 where it is pumpedunder pressure to injection loop 4 within reaction zone 5. The moltenadipic acid under high pressure is joined at injection loop 4 bycont-rolled volumes of refined hexamethylenediamine under equal pressurewhich has been fed from hexamethylenediamine melter 6 by line 7 to pump8.

In a typical example the molten adipic acid and refinedhexamethylenediamine melters may be steam jacketed vessels containing ameans for agitating or stirring the contents thereof. The temperature ofthe adipic acid within the adipic acid melter may be between 160 C. and200 C. and the temperature of the hexamethylenediamine may be between 20C. and 50 C. Inert gas pressure may be applied to the contents of eithervessel if desired.

Pumps 3 and 8 may be of any type suitable for handling hot liquids andcapable of delivering controlled volumes of the hot liquid at pressuresup to 2500 pounds per square inch. A typical example of a suitable pumpis a Zenith type gear pump provided with steam tracer lines around thepump body. Steam tracer lines may be provided around all lines leadingfrom the melters to the pumps and from the pumps to the reaction zone ifneeded to maintain the adipic acid and the hexamethylenediamine in thedesired temperature ranges.

Because of the well-known action and reaction of the molten adipic acidand the refined hexamethylenediamine when these compounds are broughttogether or mixed in high concentrations, the injection loop 4- providesa means for mixing substantially pure molten adipic acid and re-' finedhexamethylenediamine in the absence of a solvent such as water so that ahomogeneous mixture free from agglomerate lumps is obtained.

The injection loop 4 may comprise any means suitable for bringing thereactant liquids together at high velocities under turbulent fiowconditions at a Reynolds number of 5000 or greater immediately upontheir joining and may be a restricting device such as a venturi sectionin the piping, a restricting orifice, or any suitable means. Reynoldsnumber, as is well known in the art, is that dimensionless quantity usedas an expression of fluid flow and is defined specifically in ChemicalEngineers Handbook, Third Edition, as edited by ]ohn H. Perry, accordingto the equation: N =DV,, wherein D is the pipe diameter, wherein V isthe linear velocity of the fluid moving therethrough, wherein p is thedensity of the fluid, and

wherein u is the absolute viscosity of the fluid. This equation definesfluid flow in full circular pipes. Modifications of the equation fordifferent shaped conduits are obvious to the art, and are set forth inPerry above.

The turbulently mixed hot reactant liquids proceed under pressure asshown by line 9 to reaction zone 5 which consists of a preheatingsection 16 and a pressure reduction section 17. The reaction zone 5 maybe any device designed to have a high surface to volume ratio for thereacting liquids, have good heat transfer properties, and be able towithstand high pressures. A device which may be suitable is a tubebundle heat exchanger with the reactant liquids passing inside the tubesand heat transfer media such as high pressure steam or Dowtherm in thearea surrounding the tubes.

In a typical example the reaction liquids within the injection loop andpreheating section of the reaction zone may be mixed in substantiallyequal volumes and are under pressures of from 1000 p.s.i.g. to 2500p.s.i.g. at temperatures from 250 C. to 400 C. For operation on acontinuous basis, the reaction zone consisting of the preheating sectionand the pressure reduction section should be designed so that thereacting liquids have a retention time therein of 10 minutes to minutes.

The reacting liquids and partially reacted polymer which has been formedin the reaction zone exit the reaction zone as shown by line 18 and passthrough pressure control means 28. Pressure control means 28 may be anydevice suitable for controlling the reactant liquid pressures within thepressure reduction zone 17 at pressures between 0 p.s.i.g. and 25p.s.i.g. and may be any manual or automatic pressure control valve whichis well known in industry.

The material of line 29 leaving pressure control valve 28 comprisesunreacted liquid adipic acid and hexamethylenediamine; partiallypolymerized hexamethylene ammonium adipate; water of reaction formedfrom the condensation polymerization of the reactants, both in theliquid and vapor phase; and hexamethylenediamine vapor. This mixtureproceeds by line 29 to vapor separator 10 wherein the primary separationof the liquid components of the mixture takes place.

In a typical example, vapor separator 10 may be a cylindrical or atruncated conical vessel wherein the mixture from line 29 is introducedsubstantially tangential to the circular cross section of the vessel andswirls around the sides of the vessel falling toward the collection heador truncated section to exit for further polymerization, and the vaporrises from the center of the vessel to be drawn off at the top thereof.Suitable means may be provided for supplying heat to the vapor separatorif desired.

Liquid polymeric mate-rial capable of undergoing further polymerizationexits from the vapor separator 10 as shown by line 12 to finisher 13wherein the final step of the polymerization process takes place.Finisher 13 may be of any design suitable for providing good heattransfer and mixing conditions to the polymer supplied thereto and manydesigns are well known in the art.

In a typical example, finisher 13 may be a horizontal screw finisheroperated at atmospheric, less than atmospheric, or greater thanatmospheric pressure with the temperature of the reaction mass thereinmaintained between 260 C. and 300 C. depending upon the polymerproperties which are desired. The dwell time of the polymer within thefinisher may be from 10 minutes to 3 hours.

Polymer with the desired properties exits from the finisher as shown byline 14 to block 15 which may comprise any subsequent polymer forming orstoring procedure such as the spinning of fibers or the banding of thepolymer with subsequent chipping for storage or blending for subsequentuse.

The disengaged vapors exiting from the top of vapor separator 10 asshown by line 11 proceed to spray condenser 19 wherein the un-reactedhexamethylenediamine vapors and entrained partially polymerized materialare condensed. Cooling Water enters spray condenser 19 by line 20 andcondenses water and hexamethylenediamine vapor and partially polymerizedmaterial which proceed from the spray condenser as shown by line 21 tofilter 22 Where the water and hexamethylenediamine are separated fromthe partially polymerized material with the condensedhexamethylenediamine and water proceeding by line 23 to crude diaminestorage 24 and the partially polymerized material being sent to Waste orother disposal by line 25. The crude diamine may be returned to standardrefining processes and fed as desired to the diamine melter 6 for reusein the process.

If desired, gas inert to the system may be fed countercurrent to theflow of the polymer in the process to aid in the removal of Water vaporand the control of the degree of polymerization of the polymer. If thisis done, gas inert to the system enters the process as shown by line 26,proceeds countercurrent to the flow of the polymer of line 12, exitsfrom the vapor separator 10 by line 11, is not condensed in the spraycondenser 19, and exits from the system by line 27 to an inert gasrecovery system for reuse or is discharged to waste.

As can be seen clearly from the above description, the process of thisinvention eliminates completely the need for adding and removing largequantities of water. This makes possible heretofore unheard of savingsin heat energy which must be supplied to the process and permits theformation of polymer with desired properties in extremely short periodsof time and a most economical manner.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it must beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claim.

What is claimed is:

A continuous substantially solventless process for the manufacture oflinear polycarbonamides characterized by high molecular weight fromhexamethylenediamine and adipic acid which comprises the steps of:

(a) melting separating substantially pure adipic acid at a temperatureof 160 C. to 180 C. and substantially atmospheric pressure;

(b) melting separately refined hexamethylenediamine at a temperature of20 C. to C. and substantially atmospheric pressure;

(0) combining continuously at a temperature of 250 C. to 400 C. and apressure of 1000 p.s.i to 2500 p.s.i substantially equal quantities ofmelted said adipic acid and melted said hexamethylenediamine under therheological condition of turbulence defined by a Reynolds number of atleast 5000;

(d) permitting combined said melted adipic acid and said meltedhexamethylenediamine to movingly reside in a preheating and reactionzone at a temperature of 250 C. to 400 C. and a pressure of 1000 poundsper square inch to 2500 pounds per square inch for a period of 10minutes to minutes;

(e) continuously subjecting material exiting the preheating and reactionzones to a pressure reduction zone operated at a pressure of atmosphericto 25 pounds per square inch, and thereafter;

(f) continuously polymerizing in a finisher the liquid material exitingthe pressure reduction zone at a temperature of 260 C. to 300 C. andsubstantially atmospheric pressure for a period of tenminutes to threehours.

References Cited by the Examiner UNITED STATES PATENTS 2,361,717 10/1944Taylor 26078 2,689,839 9/1954 Heckert 26078 2,840,547 6/1958 Stump 26078WILLIAM H. SHORT, Primary Examiner.

H. D. ANDERSON, Assistant Examiner.

